The present invention relates to the field of electronic devices and manufacturing methods, and, more particularly, to methods for making and devices such as including packaged integrated circuits.
Integrated circuits are widely used in many types of electronic equipment. An integrated circuit may include a silicon substrate in which a number of active devices, such as transistors, etc., are formed. It is also typically required to support one or more such integrated circuits in a package that provides protection and permits external electrical connection.
As the density of active devices on typical integrated circuits has increased, dissipation of the heat generated has become increasingly more important. Designers have developed cooling techniques for integrated circuits based on micro-electromechanical (MEMs) technology.
For example, as shown in FIG. 1, a prior art electronic device 10 includes a package 11 including a first member 12 comprising silicon, and a second member 14 comprising a low temperature co-fired ceramic (LTCC) material. The first member 12 may include several stacked silicon substrates 12a, 12b having various components of a micro-fluidic cooler formed therein. For example, as shown in the illustrated embodiment, an evaporator 16 and condensor 17 may be provided and interconnected via one or more micro-fluidic channels or passageways 21 formed between the silicon substrates 12a, 12b. One or more MEMs pumps, not shown, may circulate the cooling fluid.
The second member 14 may also include several LTCC layers 14a, 14b laminated together as shown in the illustrated embodiment. The second member 14 also illustratively carries an integrated circuit 22, such as an insulated gate bipolar transistor (IGBT) or other integrated circuit that may typically generate substantial waste heat. The second member 14 also includes external connections 23 which are connected to the electrical connections 24 of the integrated circuit 22 via the illustrated wires 25.
As shown in the enlarged view of FIG. 2, the integrated circuit 22 is carried by a receiving recess 27 in the second member 14. A series of micro-fluidic passageways 30 may be provided through the LTCC member 14 adjacent the integrated circuit 22 to deliver cooling fluid thereto.
Typically, the LTCC member 14 and the silicon member 12 are adhesively joined together as schematically illustrated by the adhesive layer 31. Thermoplastic and/or thermosetting adhesives are commonly used. Metal layers may also be used. Unfortunately, the adhesive layer 31 has a number of shortcomings. The adhesive layer 31 may not typically provide a hermetic seal at the interface between the silicon and LTCC, thus, cooling fluid may be lost. In addition, the adhesive layer 31 may also provide yet another layer through which the heat must pass. Of course, it may be difficult to provide an adhesive layer 31 which is uniform and which does not protrude into the interface or otherwise block or restrict the flow of cooling fluid. In other words, such an adhesive layer 31 unfortunately provides only non-hermetic and non-uniform bonding the members.
U.S. Pat. No. 5,443,890 to Ohman discloses a leakage resistant seal for a micro-fluidic channel formed between two adjacent members. A sealing groove is provided and filled with a fluid sealing material which is compressed against adjacent surface portions of the opposing member. The provision for such a sealing structure requires additional manufacturing steps and may not be suitable for many applications.
In view of the foregoing background, it is therefore an object of the invention to provide a method and associated electronic device wherein LTCC and silicon members are bonded together to form a hermetic seal with uniform bonding.
This and other objects, features and advantages in accordance with the present invention are provided by a method for making an electronic device comprising positioning first and second members so that opposing surfaces thereof are in contact with one another, the first member comprising silicon and the second member comprising a low temperature co-fired ceramic (LTCC) material. The method also includes anodically bonding together the opposing surfaces of the first and second members to form a hermetic seal therebetween. The anodic bonding provides a secure and uniform bond between the members.
The first and second members may have substantially planar major opposing surfaces. The anodic bonding provides a uniform bond across these surfaces to reduce possible stress effects which may otherwise occur due to the difference in thermal coefficients of expansion of the two different materials.
Anodically bonding may comprise applying a voltage across the first and second members, applying pressure to the opposing surfaces of the first and second members, and/or heating the first and second members. The method may also include cleaning the opposing surfaces of the first and second members prior to anodically bonding the members.
The method may further include forming at least one cooling structure in at least one of the first and second members. More particularly, the least one cooling structure may comprise at least one first micro-fluidic cooling structure in the first member, and at least one second micro-fluidic cooling structure in the second member aligned with the at least one first micro-fluidic cooling structure. The at least one first micro-fluidic cooling structure may comprise an evaporator and the at least one second micro-fluidic cooling structure may comprise at least one micro-fluidic passageway. Anodic bonding permits a hermetic seal between the two members, and significantly reduces or eliminates the loss of cooling fluid at the interface between the two members which could otherwise occur.
The method may also include positioning at least one integrated circuit adjacent the at least one cooling structure, such as adjacent the at least one micro-fluidic cooling passageway in the second member. The at least one integrated circuit may comprise electrical connections, and the second member may carry external electrical connections connected to the electrical connections of the at least one integrated circuit.
For typical electronic devices, the anodically bonding may comprise applying a voltage in a range of about 500 to 1000 volts across the first and second members. Similarly, the anodically bonding may comprise applying pressure in a range of about 1 to 20 psi to the opposing surfaces of the first and second members. Continuing along these lines, the anodically bonding may comprise heating the first and second members to a temperature in a range of about 100 to 150xc2x0 C.
Another aspect of the invention relates to an electronic device, such as a multi-chip module (MCM) or other similar packaged integrated circuit, for example. The electronic device may comprise a first member comprising silicon, and a second member comprising a low temperature co-fired ceramic (LTCC) material. Moreover, the first and second members have opposing surfaces thereof anodically bonded together to form a hermetic seal therebetween. The first and second members may have opposing generally planar major opposing surfaces, for example.
At least one of the first and second members may comprise at least one cooling structure. For example, the first member may comprise at least one first micro-fluidic cooling structure therein, such as an evaporator. In addition, the second member may further comprise at least one second micro-fluidic cooling structure aligned with the at least one first micro-fluidic cooling structure of the first member. For example, the at least one second micro-fluidic cooling structure may comprise at least one micro-fluidic passageway.
The electronic device may also include at least one integrated circuit adjacent the at least one second micro-fluidic cooling structure of the second member. The at least one integrated circuit may also comprise electrical connections. Accordingly, the second member may comprise external electrical connections connected to the electrical connections of the at least one integrated circuit.